Among the various embodiment in the art of tandem axle suspensions used in trucks, trailers and semi-trailers, it stands out the suspensions using a spring pack mounted on each axle and longitudinally interconnected by means of load equalizers housed on the chassis hangers of the vehicle, which are commercially referred to as mechanical suspension.
The constructive forms of these suspensions using equalizers, spring pack and chassis hangers come in several models using equalizer bearings built in different shapes, usually cylindrical, provided with pins, bushings, bearings and corresponding attachments.
The most used equalizer pivots comprise pins and metal bushings and are provided with lubrication means.
Said lubrication-dependent equalizer pivots are subject to considerable wear caused by friction between the parts that rotate on an oscillating semi-revolving form, at an angle close to 20° and on the area where the load is concentrated. Because of this, lubrication becomes poor due to the high pressure between the parts, the constant presence of contaminants and abrasive materials from dirt roads, and the precarious sealing conditions of the bearing, which results from a gradual process of wear.
There exist also cases of equalizer pivots using self-lubricating bushings, wherein more appropriate sealing becomes necessary, making it complex and costly.
The systems using journal bearings with bearings and where sealing is better also need lubrication, depending on the type of bearing used. In this case, wear on the bearing race also takes place on the area where load is concentrated due to the small rotating angle of the equalizer.
There are other systems of equalizer pivots that do not use lubrication since they are provided with rubber bushings or elastomeric cushions, allowing elastic deformation so that the equalizer may articulate relative to the bracket.
In this case, more space is needed for the bearing due to the low resilience of the material, and this is a drawback. Due to elasticity, they allow lateral movement of the equalizer relative to the bracket, requiring the use of mechanical stops to retain this movement, which ultimately increase their cost.
In addition, these brackets and equalizers must also have fixing pins or screws that ultimately make assembly more difficult. In case said brackets are welded to the chassis of the vehicle, the equalizer must be mounted to the bracket following the welding and painting processes, which, likewise, results in ergonomically undesired tasks that make assembly time longer.
The systems described above can be viewed in the art of the illustrative drawings, in FIGS. 9, 9a, 9b, 10, 10a and 10b. 
The document BRMU8601825-2 describes a constructive arrangement applied to the equalizer of mechanical tandem suspensions, used in commercial vehicles, equipped with stamped sides, support shoes, said support shoes projecting beyond the sides, said sides being joined by welding, polymeric sliding pads mounted on the sides, metal tube, wherein the elastic bushing is mounted, said elastic bushing being either a separate part or a piece attached to the equalizer, the elastic element being vulcanized to the metal or non-metal covers of the bearing and/or directly to the metal pipe.
The document described above presents as advantages the significant increase in the durability of the balance and in its pivoting system, increased reliability, and acts as a filter for the high vibration caused to the equalizer, said equalizer being, furthermore, provided with polymeric pads for lateral sliding with the bracket.
The drawback in relation to this system, although with advantages over the previous technique, is the high cost thereof, the complexity of its assembly, in addition to the difficulty in obtaining a proper torque on the axial attachment of the elastic bushing with the bracket.
The document BRPI0802402-2 describes an equalizer with a non-cylindrical bearing for a tandem axle suspension, said tandem axle suspension being basically provided with a metal frame, said metal frame comprising an equalizer, said equalizer being provided with a non-cylindrical oscillating bearing in the middle area, said bearing being surrounded by an elastomeric bushing or of any other material with equivalent characteristics, said bushing being provided with an internal bushing element, which can be in a more rigid extension of the same material or by any other material, both with non-cylindrical geometric shapes, for the attachment of the equalizer to the frame of the vehicle or to the hanger brackets of the suspension, by means of screws or any other means of attachment, being also provided, at the ends of said equalizer, seats for the tips of the springs, said spring seats being defined by a succession of matching radii.
The document described above brings, as advantages, optimization in the shape of the bushing relative to the load applied and to the inner space of the equalizer, improvement in comfort and in the transmission of noise to the vehicle, in addition to not requiring lubrication.
The drawback in this system, although offering advantages over the system described in the previous document, is still the high cost of the bushing provided with elastomeric, due to its complexity, impacting on the cost of replacement and also on the need of stops to retain the lateral displacement relative to the bracket, as earlier explained.
Among the problems found in the hanger brackets and equalizers of the art of tandem suspensions, we highlight, as the most relevant ones, the disadvantage of having too many and different components that are complex and subject to premature wear, requiring periodic maintenance, in addition to the need to use precise torque bands on the mounting brackets, these mounting brackets being difficult to control, not to mention that they may cause components to fail in use.
Said brackets and equalizers, due to the diversity and complexity of their components and processes, are more subject to failures in their manufacturing and assembly during the various steps of their production process, these production processes ranging from the purchase of components to the installation in the vehicle, having the potential of worsening the problems mentioned above.
Another drawback in the current hanger brackets and equalizers is that they are provided with various types of materials and require many steps in their manufacturing process, which ultimately increases their cost.
Another deficiency found in the cited art of equalizers is structural discontinuity due to the presence of bushing or bearing housed inside the body, the body being usually welded, or even cast, wherein there is the need to provide, around said cast body, structural elements to remedy this discontinuity, which makes the equalizer heavier and costly.
Another drawback is the need of conducting maintenance procedures more frequently due to the fact that their components are more subject to wear, resulting in a high maintenance cost.
It is, therefore, a need in this art to provide new central hanger brackets and equalizers for tandem suspensions, these central hanger brackets and equalizers being simple in their construction process, easy to mount and resilient to wear, with a fewer number and type of components, which ultimately results in better performance and lower cost of the product.
These new central hanger brackets and equalizers in a tandem suspension will also contribute to facilitate the processes of production, storage, transport logistics, and mounting of the suspension on the vehicle, due to their simplicity and fewer number and type of components.